Topic: cb550k1 mid revs issue

[Simon_PL]

hallo there,
Writting this I'm hoping not to be banned as this issue seems to be quite common here. Nevertheless after many posts read here I'm not able to get the clue. I have 1975 cb550k1 with 022A carbs. The engine has been completly rebuild and chcecked, carbs cleaned and the jets had been changed for new ones but the same size. The ignition is OEM , coils are 4,6Ohms from 4ino1, breakers are genuine, from Davis Silver Spares. Pipes where Jardine 4->2 but also lately changed them to reproduction 4->4 from CMS. There is no problem with the fuel filter or tank. All this is useless. Short after 4000rpm I'm having this breakdown and it hard to get through 5500, it acts like a rev limiter. It is not possible to get to the 8 or 9k rpm. Films are made in standing position but while riding it is pretty much the same.
What else is to be chceked? Are these new jets first to get rid of?

regards
Simon

[Scott S]

 Genuine Keihin jets are the first things I'd try. What needles and emulsion tubes are you using?

[jaytee-nz]

Have you checked that all the clips that hold the main jets in place are still secure ?

[dave500]

set the points with a dwell meter and timing with a dynamic timing light,watch the advance with the light as you increase rpm till it stops advancing,set the timing to that second advance mark,forget where it ends up when idling,once thats done then fiddle with the carbs.

[Deltarider]

Difficult one. Allow me some questions. What do sparkplug noses look like? Any discolouring at the headers? What is the air intake situation? You mention a 4-4 exhaust, but I have not seen one muffler, let alone 4.
Some observations. I'm not sure how accurate your tach is. It seems a bit hesitant which usually indicates a cable problem. Are you sure rpms are not higher than indicated? When in doubt, take inner cable out, clean with kerosene and grease with some lithium grease. Revs drop a bit on the slow side when slides are down. Apart from a hesistant tach, it could indicate lean mix, sometimes caused by airleaks or aftermarket (foam) airfilter elements. Could also have its cause in an advancer not working correctly. So, as Dave already suggested, check advancer is working as it should. BTW, I can't say I hear it, but it takes only a few seconds to check for unwanted - often intermittent - arcing at the points and between plugcaps and the head. Ignition always comes first. When in doubt, shoot a video of the points.

[Scott S]

 After watching the video, are you sure the tach is right? I think it's revving higher than you think!

[Deltarider]

After watching the video, are you sure the tach is right? I think it's revving higher than you think!

I also had the impression. BTW, I would NOT rev it that high at the stand.

[Simon_PL]

ok, thank you , I'll do the homework. Films had been taken when I had taken off end muffers (4->2 jardine) for checking would this had any impact on bike. Anyhow I will chceck the cable and points once again. Are Keihin jets available to buy nowadays?

Simon

[RickThomas]

After watching the video, are you sure the tach is right? I think it's revving higher than you think!

I also had the impression. BTW, I would NOT rev it that high at the stand.

+1 to both.
Those gauges look pretty good, so I would bet that they have been rebuilt. I just got a recently rebuilt tachometer in a part lot that wouldn't rev smoothly. Opened it up and found that the rebuilder had used very tacky (and perhaps too much) lube on the bell. Relubed it properly and the problem was gone.
Although, there does sound like a bit of hesitation at the high end. A better test is on the roadway under load. It may be the timing or the points. Can't recommend a transistorized ignition like Hondaman's enough!

[Simon_PL]

It took some time but did some homework. Problem still appears and all my shots are mi#$%*.
For now I'm looking for the reason somewhere around the ignition but to be honest I wander in the fog.
Revmeter issue is a secondary problem - yes, it might show wrong revs or go crazy but the primary problem is the lac of power, torque and improper engine's work. Nevertheless I replaced old one which apparently was slighlty cracked(cable + armour). That gave non effect.
It is hard to describe bu in the mid or high revs the engint work is a bit similar like 2-stroke engine, revs have lot of small, short cutdowns. Also any attempt of acceleraction from low revs on higher gear gives effect of cutdown power and jerking of he revs. I undersand its an 40YO bike and not an XJR1300 or some other  big 4cylinder but I've seen plenty of mouvies of cb550 and it's definitely smth wrong about mine.
What I did from last time:
1. Checked and adjust ignition timming once again (static way)
2. Tried to adjust ignition timming dynamic way but - surprise - induction clamp worked only on cylinders 2&3. On 1&4 lamp wasn't give any light even there obviously was an ignition on 1&4th cylinder.
3. Checked coils - on primary side both where 4,9-5 Ohms (both are relativly new , ~1 y.o.) but on secondary side I have no ressitnace at all - on any of all 4 spark plg wires, the same with dismounted sparkplug cap - nothing.
4. I thought - maybe grounding. Engine, castings had been lately renoveted , laquert so maybe points have some ground disruptrion, so took out points,scrached some very thin layer , put all back togheter, adjust. Nothing.
5. My last action was to install Hondaman's module, which I did. I noticed sligtly better , more "juicy" work of the engine , bu again - I took the road , went to higher revs and problems appeared unchanged.

2nd film is after points 4 and 5.

all records are "full throttle" especially on the beginning.

Any ideas are really welcome.

[HondaMan]

I'm placing my bets on the jets.
The Keyster jets (or other aftermarket jets) are all very lean for their number. For example, if your original mainjet was #98 and you installed a Keyster #98, it will act like a #88 or so. This is the same situation as in the 750. This will make the midrnage VERY flat and lean. Your plug looks like that, too.

[Deltarider]

On 1&4 lamp wasn't give any light even there obviously was an ignition on 1&4th cylinder.

Have you tried flipping the induction clamp? There is polarity to observe! On our waste spark systems, induction clamp works only in one position, the right one for that HT lead, so ignore 'THIS SIDE TOWARDS PLUG'.

[Scott S]

Genuine Keihin jets are the first things I'd try. What needles and emulsion tubes are you using?

 Order genuine Keihin jets and, if you have them, put the stock emulsion tubes and needles back in.

[Simon_PL]

are Keihin jets still available ? JetsRus is the right place?

Simon